message_thread_id = self._extract_message_thread_id(update)
if not message_thread_id:
    await self._reject_for_thread_mode(...)
    return False

@staticmethod
def _extract_message_thread_id(update: Update) -> Optional[int]:
    message = update.effective_message
    if not message:
        return None
    message_thread_id = getattr(message, "message_thread_id", None)
    if isinstance(message_thread_id, int) and message_thread_id > 0:
        return message_thread_id
    dm_topic = getattr(message, "direct_messages_topic", None)
    topic_id = getattr(dm_topic, "topic_id", None) if dm_topic else None
    if isinstance(topic_id, int) and topic_id > 0:
        return topic_id
    # Telegram omits message_thread_id for the General topic in forum groups;
    # its canonical thread ID is 1.
    chat = update.effective_chat
    if chat and getattr(chat, "is_forum", False):
        return 1
    return None